I have seriously considered becoming DDs NRP and placing primary care of DD in her Dads hands on a number of occasions.
He is an incredibly difficult person to deal with and time and time again has disrupted DD in order to secure the 'equality' he believes that he is entitled to.
We have 50:50 of DD but, currently, her primary address is with me. That hasn't stopped him redirecting her mail, changing her address with the GP/school, cancelling childcare arrangements, and generally being a complete arse. His current campaign (regarding school transport) could lead to issues of eligibility for the school - great move, Dad!
Some of it is his desire to control me; he demands we meet and speak face to face frequently (he would prefer daily but would accept weekly) because we are co-parenting; he regularly expresses his disappointment in my words and behaviour, and he undermines my parenting at every opportunity.
When he becomes particularly relentless, it often seems that the best solution would e to give him what he wants (DD) 
Now she is older, it is a lot easier - but had she been a toddler when we split, I think I would have crumbled by now and handed over primary care in order to continue enjoying DD's company when I could, rather than constantly undoing damage 